1. Field of the Invention
The present invention relates to an automotive electric power steering controller that uses an electric motor to generate torque for assisting driver""s steering force to thereby supplement the steering force supplied to the steering system. The invention also relates to a method of controlling this electric power steering controller.
2. Description of the Related Art
FIG. 14 is a block diagram showing the structure of the prior art electric power steering controller described, for example, in Japanese Patent Laid-Open No. 186994/1995. This controller has a steering torque detector 1 for detecting steering torque when the driver steers. A steering torque controller 2 calculates an assisting torque based on the output from the steering torque detector 1 and produces an output signal indicating the calculated assisting torque. A motor speed detector 3 detects the speed of an electric motor. A damping compensator 4 calculates and produces a damping compensation signal based on the motor speed detected by the motor speed detector 3. A motor acceleration detector 5 detects the acceleration of the motor using the output from the motor speed detector 3. An inertia compensator 6 calculates and produces an inertia compensation signal based on the motor acceleration detected by the motor acceleration detector 5. A judging unit 7 makes a decision as to whether the output from the steering torque detector 1 and the output from the motor speed detector 3 are identical in sense and supplies the result of the decision to all of the steering torque controller 2, the damping compensator 4, and the inertia compensator 6. A first adder 8 produces the sum of the assisting torque signal, the damping compensation signal, and the inertia compensation signal. This sum is referred to as the target torque. A motor current determiner 9 calculates and produces a target current signal from the target torque. The aforementioned motor is indicated by numeral 10, produces a motor current value corresponding to an applied voltage, and generates an assisting torque that is roughly in proportion to the motor current value, thus driving the steering mechanism. A motor current detector 11 detects the current value of the motor 10. A second adder 12 finds the difference between the target current signal produced by the motor current determiner 9 and the motor current value detected by the motor current detector 11. A motor driver 13 determines a voltage applied to the motor 10 according to the error between the target current signal calculated by the motor current determiner 9 and the motor current value detected by the motor current detector 11 and applies the determined voltage to the motor 10. A vehicle speed detector 14 detects the speed of the vehicle and sends a signal indicating the detected vehicle speed to all of the steering torque controller 2, damping compensator 4, and inertia compensator 6.
The operation of the prior art electric power steering system constructed in this way is now described. When the driver of the automobile steers the steering wheel, the produced steering torque is measured by the steering torque detector 1 and sent to the steering torque controller 2. This torque controller 2 calculates the assisting torque that is roughly in proportion to the output signal from the steering torque detector 1 and drives the motor 10 according to the assisting torque signal. In this way, the motor supplements the driver""s steering torque. Consequently, the steering torque that the driver must produce is alleviated.
At this time, the judging unit 7 makes a decision as to whether the output from the steering torque detector 1 and the output from the motor speed detector 3 are identical in sense. If they are identical, neither the damping compensator 4 nor the inertia compensator 6 is operated; only the steering torque controller 2 is operated. The steering torque controller 2 determines the assisting torque signal according to both output from the steering torque detector 1 and vehicle speed signal from the vehicle speed detector 14. The target torque is determined from this determined assisting torque signal. The motor current determiner 9 determines the motor driving current.
If they are not identical, the steering torque controller 2 is not operated; the damping compensator 4 and the inertia compensator 6 are operated. The target torque is determined from the output from the damping compensator 4 and from the output from the inertia compensator 6. The motor current determination unit 9 determines the motor driving current. If the vehicle speed is low, the target torque is made identical in direction with the rotation of the motor. If the vehicle speed is high, the target torque is made opposite in direction to the rotation of the motor. Accordingly, when the driver is steering the steering wheel, the electric power steering system supplements the driver""s steering torque to alleviate the torque necessary for the steering. When the driver is returning the steering wheel, if the vehicle speed is low, the electric power steering system assists the steering wheel to return to its center position. If the vehicle speed is high, the motor 10 is so controlled that the steering wheel is prevented from returning to its center position at an excessively high speed.
Generally, the driver steers when the vehicle turns round road curves or across road junctions and then the vehicle returns to straight-line driving. At this time, he or she returns the steering wheel by making use of spontaneous returning force of the steering wheel owing to reaction torque applied from the road surface through the tires. However, when the vehicle speed is low or the steering wheel is rotated through only a small angle during high-speed driving, the reaction torque applied from the road surface through the tires is weak and so the reaction torque is less than the frictional torque within the steering mechanism. Therefore, the steering wheel often does not return to its center position when the vehicle returns to straight-line driving. In this case, accordingly, the driver must apply torque to the steering wheel in returning the steering wheel. Consequently, the steering feeling deteriorates.
To cope with this problem, the prior art technique makes a decision as to whether the output from the steering torque detector 1 and the output from the motor speed detector 3 are identical in sense at low vehicle speeds. If they are not identical, the motor driving current is so set that the motor 10 is rotated in the forward direction. In this way, the returnability of the steering wheel at low vehicle speeds is improved.
In the prior art technique, when the driver steers while the reaction torque applied from the road surface through the tires is small as encountered when the vehicle turns a junction at a low speed or when turns a curve of a mildly winding road at a high speed, the steering wheel is kept stationary unless the driver applies torque in a direction to return the steering wheel. Hence, the motor 10 does not rotate. At this time, the judging unit 7 cannot judge whether the output from the steering torque detector 1 and the output from the motor speed detector 3 are identical or not. Consequently, the motor driving current cannot be so set that the motor is rotated in the forward direction. Hence, the returnability of the steering wheel cannot be improved.
Furthermore, in the prior art technique, the motor driving current is only allowed to be so set that the motor is rotated in the reverse direction. In consequence, the returnability of the steering wheel cannot be improved.
The present invention has been made to solve the foregoing problems.
It is an object of the present invention to provide an electric power steering controller which is for use in a vehicle and which permits the driver to return the steering wheel to its center position without applying torque in the direction to return the steering wheel when the driver steers while reaction torque applied from the road surface through the tires is small as encountered when the vehicle turns a junction at a low speed or when the vehicle turns a curve of a mildly winding road at a high speed. The steering controller controls the returning steering wheel using a steering angle corresponding to driver""s will and can improve the returnability of the steering wheel under every driving condition.
It is another object of the invention to provide an electric power steering controller capable of coping with faults of sensors if such faults occur.
It is a further object of the invention to provide a method of controlling such an electric power steering controller.
According to this invention an electric power steering controller mounted in an automobile and using torque generated by an electric motor to supplement driver""s steering torque, said electric power steering controller comprising:
a steering torque detection means for detecting the steering torque applied by the driver;
a steering angle detection means for detecting a steering angle;
a first road reaction torque estimation means for estimating a first road reaction torque that tires receive from the road surface using the steering torque detected by the steering torque detection means;
a second road reaction torque estimation means for estimating a second road reaction torque using the steering angle detected by the steering angle detection means; and
a returning torque compensation means for controlling the assisting torque of said electric motor in a direction to return the steering wheel to its original position according to the second road reaction torque estimated by the second road reaction torque estimation means, said returning torque compensation means judging that the steering angle detection means is at fault when a difference between the first road reaction toque and the second road reaction torque is greater than a given value.
According to this electric power steering controller, the returnability of the wheel can be improved under any operating conditions.
Furthermore, the electric power steering controller wherein said returning torque compensation means judges that there is a fault when a difference between two estimated road reaction torques is kept greater than a given value for a given time.
According to this electric power steering controller, the the power steerinng controller assures detection of a fault if such a fault is present.
Furthermore, the electric power steering controller wherein there is further provided a steering speed detection means for detecting a steering speed, and wherein said returning torque compensation means judges that there is a fault when the steering speed detected by said steering speed detection means is less than a given value and, at the same time, a difference between two estimated road reaction torques is greater than a given value.
According to this electric power steering controller makes the decision operation reliable.
Furthermore, the electric power steering controller wherein said returning torque compensation means judges that there is a fault when the first road reaction torque is greater than other estimated road reaction torque by more than a given value.
According to this electric power steering controller assures that such a fault is detected.
Furthermore, the electric power steering controller wherein said returning torque compensation means judges that the motor has locked when the first road reaction torque is kept greater than other estimated road reaction torque by more than a given value for a given time.
According to this electric power steering controller makes the reliable the operation to judge whether the motor has locked.
Furthermore, the electric power steering controller wherein said returning torque compensation means has a function of judging road conditions and wherein, if the returning torque compensation means judges that a road surface condition is a non-high friction, any decision as to whether the detection means are at fault is not made.
According to this electric power steering controller decisins as to whether the detection means are at fault are made depending on the road surface condition.
In addition, an electric power steering controller mounted in an automobile and using torque generated by an electric motor to supplement driver""s steering torque, said electric power steering controller comprising:
a steering torque detection means for detecting the steering torque applied by a driver;
a lateral acceleration detection means for detecting lateral acceleration of the automobile;
a first road reaction torque estimation means for estimating a first road reaction torque that tires receive from the road surface using the steering torque detected by the steering torque detection means;
a third road reaction torque estimation means for estimating a third road reaction torque from the lateral acceleration of the automobile detected by said lateral acceleration detection means; and
a returning torque compensation means for controlling the assisting torque produced by said electric motor in a direction to return the steering wheel to its original position according to the third road reaction torque estimated by said third road reaction torque estimation means, said returning torque compensation means judging that the lateral acceleration detection means is at fault when a difference between the first road reaction torque and the third road reaction torque is greater than a given value.
According to this electric power steering controller, the returnablility of the steering wheel can be improved under every operating condition, and the power controller can cope with fault in lateral acceleration detection mean if such faults are present.
In addition, an electric power steering controller mounted in an automobile and using torque generated by an electric motor to supplement driver""s steering torque, said electric power steering controller comprising:
a steering torque detection means for detecting the steering torque applied by the driver;
a yaw rate detection means for detecting yaw rate of the automobile;
a first road reaction torque estimation means for estimating a first road reaction torque that tires receive from the road surface using the steering torque detected by said steering torque detection means;
a fourth road reaction torque estimation means for estimating a fourth road reaction torque from the yaw rate of the automobile detected by said yaw rate detection means; and
a returning torque compensation means for controlling the assisting torque produced by said electric motor in a direction to return the steering wheel to its original position according to the fourth road reaction torque estimated by said fourth road reaction torque estimation means, said returning torque compensation means judging that the yaw rate detection means is at fault when a difference between said first road reaction torque and said fourth road reaction torque is greater than a given value.
According to this electric power steering controller, the returnability of the steering wheel can be improved under every operating condition,and the power steering controller can cope with a fault in the yaw rate detection means if such a fault is present.
In addition, an electric power steering controller mounted in an automobile and using torque generated by an electric motor to supplement driver""s steering torque, said electric power steering controller comprising:
a steering torque detection means for detecting the steering torque applied by the driver;
a first road reaction torque estimation means for estimating a first road reaction torque that tires receive from the road surface using the steering torque detected by said steering torque detection means;
a fifth road reaction torque detection means for detecting a fifth road reaction torque; and
a returning torque compensation means for controlling the assisting torque produced by said electric motor in a direction to return the steering wheel to its original position according to the fifth road reaction torque detected by said fifth road reaction torque detection means, said returning torque compensation means judging that any one of the road reaction torque detection means is at fault when a difference between the first road reaction torque and the fifth road reaction torque is greater than a given value.
According to this electric power steering controller renders reliable the decision made as to whether the road reaction torque is abnormal.
Furthermore, the electric power steering controller wherein said returning torque compensation means judges that there is a fault when the first road reaction torque is kept greater than the fifth road reaction force by more than a given value for a given time.
According to this electric power steering controller decisions as to whether the detection means are at fault are made depending on the road condition.
In addition, a method of controlling an electric power steering controller mounted in an automobile by using torque generated by an electric motor to supplement driver""s steering torque, said method comprising the steps of:
estimating a first road reaction torque using the steering torque;
estimating a sixth road reaction torque using any one of a steering angle, lateral acceleration of the automobile, and yaw rate of the automobile detected by detection means;
controlling the assisting torque of said motor in a direction to return a steering wheel to its center position according to the estimated sixth road reaction torque; and
making a decision based on a difference between said first road reaction torque and said sixth road reaction torque as to whether said detection means are at fault.
According to this method of controlling an electric power steering controller, the returnability of the steering wheel can be improved under every operating condition, and the power steering controller can cope with a fault in the detection means if such a fault is present.
Furthermore, a method of controlling an electric power steering controller, wherein it is judged that there is a fault when a difference between the first and sixth road reaction torques is kept greater than a given value for a given time.
According to this method of controlling the electric power steering controller assures detection of a fault in the detection means if such a fault is present.
Furthermore, a method of controlling the electric power steering controller, wherein road conditions are judged, and wherein, if the road surface condition is a non-high friction, any decision as to whether the detection means are at fault is not made.
According to this method of controlling the power steering controller, a decision as to whether the detection means are at fault can be made depending on the road surface condition.
Other objects and features of the invention will appear in the course of the description thereof, which follows.